Bulk cargo carrying wheeled vehicles such as railroad hopper cars are usually constructed to discharge bulk cargo either in a controlled discharge or in an uncontrolled discharge. Typically, a carload of wheat or other grain must be discharged in a controlled manner for proper handling. Conversely, bulk cargo such as coal and crushed stone or gravel are usually dumped from a railroad car in an uncontrolled discharge.
The mechanism for providing a controlled discharge is necessarily quite different from that required for uncontrolled discharge; and heretofore no simple and inexpensive means has been devised for unloading a bulk cargo selectively either in a controlled manner or an uncontrolled manner.
A dual discharge hopper -- i.e., one which can discharge bulk cargo either in a controlled manner or an uncontrolled manner, is very desirable because it permits a bulk cargo carrying vehicle to be used with a much wider variety of bulk cargos than can any car which is capable of being discharged only in one of the two ways. One of the reasons that there is frequently a shortage of railroad cars for moving grain at harvest time is that there is little use for such cars at any other time; and the railroads cannot afford to keep a huge stock of controlled discharge bulk cargo cars if they must be inactive most of the year.
Applicant is aware of only two dual discharge hopper structures, which are those disclosed in U.S. Pat. No. 3,396,675 and 3,511,188. Each of them discloses a relatively complex system in which a hopper has a linkage mounted bottom closure for free discharge of material, and on the linkage mounted closure is a crank operated, controlled discharge closure. While such structures function satisfactorily, they are relatively complex and expensive.